Chaeles hall



(No Model.)

0. BALL.

SCREW.

No. 338,956. Patented Mar. 30, 1886.

MY mm. m:

UNITED STATES PATENT OFFICE.

CHARLES HALL, on NEW YORK, N. Y.

SCREW.

SPECIFICATION forming part of Letters Patent No. 338,956, dated March 30, 1886.

Application filed October 12, 1885. Serial No. 179,620.

To all whom it may concern:

Be it known that 1, CHARLES HALL, of the city and State of New York, have invented an Improvement in Lag-Screws, of which the following is a specification.

Lag-screws have been made with a single thread and with a reduced and tapering point; but such screws have had a different character of thread to the one employed by me, and difficulty has been experienced in driving the same, because the end of the screw-thread forms a cutting-lip at one side only of the point. For this reason such lip becomes a resistance that tends to divert the screw from its perpendicular position, and when the screw is rotated, the lip, acting at one side only and being unbalanced, prevents the screw acting with uniformity in cutting its way into the wood. In other instances an ordinary single-threaded screw has been intersected by two or more spiral channels at a slight inclination to the axis of the screw; but the numerous intersectingpoints tended to injure the wood.

My invention relates to a lag-screw having two threads cut in its cylindrical body, the upper surfaces of the threads being perpendicular, or nearly so, to the axis of the screw, and the lower surfaces of such threads being at an inclination to the axis, so that such threads will drive easily into the wood and hold firmly against any effort to withdraw the screw, and the point of the screwis a cone intersecting the screw-threads and forming two cutting-lips at the base of the cone, such cutting-lips being in the line of the radius, or nearly so, in order that the ends of the screwthreads may cut their own way into the wood when thelag-screw is rotated to screw it home to place after having been driven partially into the wood.

In the drawings, Figure 1 is an elevation of the screw. Fig. 2 is an end view of the same, and Figs. 3 and at are elevations of the point of the screw on a magnified scale.

The headAis usually square. The body B is cylindrical, and into the same are cut channels forming two screw-threads. The upper edge, 0, of each screw-thread is preferably perpendicular, or nearly so, to the axis of the (No model.)

screw. The portion at of each screw-thread is at an inclination, and the portion 6, forming the bottom of the channel between the screwthreads,is preferably parallel, or nearly so, to the axis. This character of screw-th read holds very firmly in the wood, and it drives easily without tearing the fiber. I however am aware that screw-threads of a similar shape to that described have sometimes been used. The point of the lag-screw is a cone running up to the portion 6 at the bases of the grooves, and fromthat place the ends of the screwthreads extend with their narrow under surfaces in planes at right angles to the axis of the screw, as seen at z. This plane intersecting the inclines of the screw-thread produces wedge-shaped cutting-edges c at the ends of the screw-threads, and the cutting-edges are in the line of the radius, or nearly so, as seen in Fig. 2. By this construction of lag-screw the resistances in driving are balanced, the conical point penetrates the wood, and the cutting-lips at opposite sides of that point displace the wood with facility, and the lag-screw is easily driven in straight to whatever extent may be desired, and when the screw is revolved to screwit home the cuttinglipsipenetrate the wood at opposite sides of the axis of rotation; hence the lag-scrcw passes in straight and freely, and the fibers of the wood are not unnecessarily injured, and there being two screwthreads the lag-screw is more rapidly screwed up to place or removed.

I claim as my invention The lag-screw having two threads with inclined surfaces at the lower sides of the threads, and surfaces that are nearly perpendicular to the axis at the upper sides of the threads, a conical point the base of which coincides with the bottom of the screw-thread, and two cutting-lips composed of the ends of the two screw -threads at opposite sides of the base of the conical point, substantially as set forth.

Signed by me this 9th day of October, A. D.

CHAS. HALL. Witnesses:

GEO. T. PINOKNEY, WILLIAM G. Mom. 

